Magnetic antenna systems



April 24, 1962 G. WENNERBERG 3,031,663v

MAGNETIC ANTENNA SYSTEMS Filed Jan. 5, 1958 3 Sheets-Sheet 1 April 24, 1962 G. WENNERBERG 3,031,663

MAGNETIC ANTENNA sYsTEMs Filed Jan. I5, 1958 3 Sheets-Sheet 2 3,9%,663 Patented Apr. 24, 1962 3,031,663 MAGNE'HC AN'EENNA SYSTEMS Gunnar Wennerberg, Paciiic Palisades, Calif., assigner, by mesme assignments, to Motorola, lne., Chicago, Ill., 1 a corporation of Hlinois Filedlan. 3, 1953, Ser. N 7il6,912 Y lll` Claims. (Cl. 343-117) receiver, or as a pair of crescent-shaped magnetic elements between which arrotatable coil is mounted. YAn antennasystem comprising such numerous parts'of course takes considerable time and pains to assemble, a factor which contributes considerably to its cost. ln addition, the use of any rotating parts in the vicinity of the surface at which the antenna is mounted necessitates strengthening of the aircraft frame in the immediate vicinity, all of which contributes to the weight and bulk of the system.

`Furthermore, inherent Vin the movement of such coils is t `a variation in their inductance, which prevents receiver tumng to the same frequency in all positions ofthe coil.

Also in the prior art, quadrantal error compensation with ferrite antennas is achievedwith undesirable structure conigurations. Different schemes fhave lbeen proposed for quadrantal error compensation in liiush mounted antenna systems; in each, two or moreferriteelements are spaced from a rotatable coil, and meansl are employed lto vary the shape vand/ or positions of such elements. Such means take the form either of ferrite stubs hired across the outer or of means to vary the spacing between the elements'. All sucharrangements require painstaking care and machining to proper dimensions, and of course add tothe weight, cost and bulk of the antenna structure. Furthermore, the inherent variations intinductance of the rotatable coil of previously known llush type antennas necessarily affect compensation; accordingly, all such means to elect quad` rantal error compensation are atjbest only approximate. It is an object of this invention to provide `a iiush mounted magnetic antenna which does not employ any moving parts, and which comprises a minimum number ofcomponent parts in a form simpler lthan any vheretofore employed. Y i Y It isanother object of this invention to provide an im.

i proved `directional antenna of the llush mounted type for Vout in the appended claims. In the drawing,

FIG. 1 is a perspective view of an antenna structure employing a square magnetic element, in accordance with thisv invention,

FIG. 2 is a schematic diagram illustrating an automatic directionnder system incorporating the antenna of FIG, l, also in accordance with this invention,

FIG. 3 is a sectional View, taken along line 3--3 of FIG. l of the structure mounted on an aircraft,

FIG. 4 is a top plan View of an antenna structure employing a circular magnetic element, also in accordance with this invention,

FIG. 5`isV a perspective view of an antenna illustrating a rectangular magnetic'element for quadrantal error compensation, in accordance `with this invention, p

FIG. 6 is a perspectiveV view of the structure of FIG. 5 mounted on an aircraft, NFIG. 7 is a sectional' View taken along-'line 7-7 of FIG. 6, f l

PEG. '8 is a plan view of a rectangular magnetic element with a modilied winding arrangement, further in accord-` ance lwith this invention, and

FIGS. 9 and l0 are plan views of different shapes of magnetic elements employing a winding arrangement as in FIG. 8. l

Referring to FIG. l, one embodiment of a magnetic antenna structure in accordance with this inventionV ern- V.l ploys a iiat square-element lil of high-frequency, highpermeability material, which may be a dust iron or ferrite slab, upon which are mounted windings 12, 14. As shown, Winding 12 is formed of apair of coils 16, 18 made of conductive ribbons Wound in one direction about ele` ment 1t); similarly, winding 14 is formed of a pair of coils 2t), 22. made of conductive ribbons ywound at right angles to Winding 12. Each coil has one end conductively connected, as by solder connections, to one end of the metallic cylinder 24 of a terminal socket centered in element 1t); the remaining ends of coils 16, 18 are connected to respective terminal pins 26, 23 and the remaining ends of coils 20, 22 are connected to respective pins 30, 32'which are xedin an insulating support 34 disposed within ring 24.' In this manner, the pairs of coils 16-18 and Ztl-Z2 are connected'in series to form the respective windings i2, 14.

. y Ring Z4 will be recognized as used as a ground connecportions of one or more of the other coils.- To prevent use in direction iinding applications on aircraft, wherein` a pair of windings form the antenna and are not subject 55 Another object of this invenion is to provide a tiredv l to variations in inductance.

directional antenna system to replace rotatable loop antenna elements heretofore employed, wherein. remote goniometer means are employed to effect translation of received signals to an ADF receiver, and wherein remote.

windings thereon, wherein said element is configured-t0 'effect quadrantal error compensation.

The above and other objects and advantages of this' invention will become apparent from the following description, taken in conjunction with theV accompanying drawing, in which "a preferred embodiment is illustrated by direct contact, insulation is provided where necessary, as by coating the conductors with suitable material, or by inserting strips of insulation material between the portions involved, or between successive layers of conductors.' 'y

Referring toy B1G. 2, connections areA made from pins 26,72% and from pins 30, 32 to the ends of respective stator windings 35, 35 of a conventional goniometer device 49;

the goniometer is mounted within the aircraft, preferably on the instrument panel in the cockpit, in a position where movement of a pointer 42 carried by its 'rotor is visible to the pilot. The rotor winding 44 of the goniometer is connected to the input of an ADF receiver 46 in aV conven-V tional manner, ,the rotor winding 44 being inductively 42, a synchro device (not shown) may be operated by motor shaft 56, from which repeater synchro means may present indications elsewhere in the aircraft.

Preferably, windings 12, 14 each have the same inductance. This is effected by proper choice of number of turns and suitably spacing the turns of the windings. Thus, since the windings are fixed, no variations in inductance can occur; further, since they are Wound at right angles to each other, there is no mutual inductance between them.

It should be noted that by placing the two windings on the same iiat ferrite element as shown, one winding 14, being wound over the other winding 12, effectively supports such other winding in assembly. However, the procedure for winding can be varied as desired; for example, the windings may be assembled in a basket-weave pattern, i.e., with their turns interlaced, so they are mutually supporting in assembly. Electrically, basket-weaving achieves symmetry as to winding capacity.

After the windings are assembled as described, the structure is mounted on the surface of the aircraft, eg., the belly of the aircraft, in a depression in the metallic yskin 6d. A suitable insulation material 62, which may be a thermoplastic resin, covers the outer surface of element 10 and, if desired, tills the crevices between the edges of the element and skin di?. The metallic ring 24 extends to the interior of the aircraft, where the electrical connections previously described are led to the goniomcter in the cockpit.

By arranging the windings on the same flat element, i.e., with their axes in the same plane, maximum effectiveness of conversion of magnetic iielcl variations in the ferrite material to electrical energy in the coils is realized. This may be better understood by considering that by so placing both windings, both are located in the vicinity of greatest concentration of magnetic lines of force. And by using element l@ as a common ferrite element to effect inducng of voltages in both windings, the irreducible minimum of magnetic elements is reached; as previously indicated, other magnetic antennas use two or more ferrite elements.

The stator windings 35, 36 of goniometer 4d are wound so as to be 90 apart electrically, as is conventional. When the transmitter station is straight ahead of the aircraft, a signal is picked up only in winding l2; the signal appearing in the output of receiver d6 causes motor 52 to position the rotor shaft so that winding 4d is at right anglesA to stator winding 35, at which point the induced signal disappears. Pointer 42 in this position indicates a null point Ialigned with the heading of the aircraft. 'lf the station is directly to the rear of the aircraft, rotor winding 44 is positioned at right angles to stator winding 35, but reversed 180 from its position when the aircraft is flying directly .toward the station. aPointer 42 in this situation would indicate that the station was 180 from null. Such ambiguity resolution will be recognized as conventional.

Similarly, for flight tangentially with respect to the transmitter, a signal would be induced in winding 14 only; the output of receiver- 46 causes motor 52 to position winding 44 at right angles to stator winding 36. Pointer 42 would here indicate that the station was at 90 or 270 from null, depending upon the direction of tangential iiight.

Where the station is to the right or left of the aircraft, -the magnetic field threads both windings and induces a signal in each; the magnitude of one signal corresponds lto the sine and -the other to the cosine of the angle lbetween the station and the aircraft. in this sitnation, motor I52 causes rotor winding 44 to assume a position between stator windings 35, 36 which corresponds to the `vector addition of `the signals. yPointer 42 here indicates the direction of the station relative to the line of ight.

Previously mentioned advantages of the system yand structure above described will be readily apparent. Further, the elimination of [any moving parts adjacent the surface of the aircraft removes Isuch troublesome problems as oil, grease and dirt flowing along the surface and into the rotatable parts to disrupt their mechanical and electrical operation.

FIG. 4 illustrates windings l2, i4 are placed on a hat circular element 7i! of ferrite. So long as the turns of the respective windings are symmetrically arranged on the element, and the windings are at right angles to each other, there is no lmutual inductance. With the same inductance for each winding, the antenna functions in the same manner as that of FIG. l.

The structures above de-scribed are useful where quadranta-l errors are not a problem; however, they are not practical where large quadrantal errors exist. The problem of quadrantal error arises in ADF operation because of the eiect of the shape of the structure (such as an aircraft) on which the antenna is mounted. For the antenna structures of FlGS. l and 4, this means that, measured from the same point in space, the Istrength of a signal induced in winding 12 during flight directly toward an A-DF station is greater than that induced in winding 4 during flight tangential to the station. The effect of the different pickup sensitivities is that if, for example, the station is 45 from the major axis of the aircraft, pointer i2 would indicate that the station is less than 45 from the line of flight. The difference between the true and apparent directions to the station is the quadrantal error.

FIGS. 5-7 illustrate an antenna structure arranged in accordance with this invention to insure complete quadrantal error compensation. This is achieved by placing windings 12, 14 on an oblong ferrite bar 3i? (in which caso the turns of winding l2 are longer than those of winding 14) having a length-to-width ratio such that the previously indicated differences in field pickup are eliminated. As in the istructures above described, windings l2, i4 have their axes in the same plane, Ithey have the same inductance, and there is no mutual inductance. The placement of ferrite bar 3d with its greater dimension parallel to the line of ight has the effect of making the pickup sensitivities of the windings the same. Therefore, for liight in any direction relative to the station, pointer 42 indicates the true direction of `the station from the heading ofthe aircraft.

FIGS. 6 and 7 illustrate an arrangement to aliix the structure of FIG. 5 to an aircraft. The structure is placed within a thin plastic housing S2, here illustrated as transparent, which is secured to the skin Gil of the aircraft, eg., by riveting. ln this case, lthe skin does not have to be modied to provide a depression in which the structure is fitted; all that is necessary is to bore a hole in which the terminal socket is inserted, and from which connections to the goniometer are made as previously described.

Between the outer surface of bar 8d and housing 82 is a thin oblong element 8d of metal. Element 84 is suiiiciently long to span `all ythe turns of winding 14, and

' is sufficiently wide to span all the turns of winding l2.

A sheet 86 of insulation material separates element $4 from the windings l2, 14. Element 84 may be the same metal as the skin of the aircraft, in which case the antenna elements are sandwiched between layers of aluminum. The effect of these layers is to minimize magnetic leakage in the vicinity of the windings and to irnprove shielding against capacitive pickup, thereby to enhance their pickup sensitivity.

A further important advantage of the compensated antenna is that, since there is no problem of variation in inductan-ces of the windings, and there is no mutual inductance, the windings and their associated structure resonate lat the same frequency in all posi-tions of the rotor lwinding of the goniometer.

FIG. 8 illustrates an arrangement for achieving quadrantal error compensation wherein wind-ings 10, 12 of equal dimensions' are wound Aacross; bar 80 so that the angle a between their axes which intercepts the major axis of bar :Sti -is bisected by suchmajor axis; Theangle a preferably is'chos'en so that for the dimensions of the ferrite element, the mutual inductance is zero. For vzero mutual inductance, angled is greater than 90, due to the effect of the ferrite.

. To further explain the arrangement in 8', it'should be noted that if the windings are centrally located on j described is reached wherein the mutual inductance is zero; as previously indicated, it has been found that this angle is greater than 90. IHowever, if .some mutual in ductance can be tolerated, as is possible in some situations, it is sufficientl if the angle a is chosen so thatthe mutual inductancemdoes not exceed the tolerable limits;

` ,such angle may begreater or smaller than 90, depending upon the coniigurationof the ferrite element. v

The proper orientation of the windings for zero or .tolerable mutual inductance" may be determined by conv `necting a Q-meter to one winding and lorienting -the windings until the Q-meter shows no change when the other winding is alternately open-circuited and short-circuited.

FIGS. 9 and 10 illustrate an arrangement wherein windings 12, 14 are positioned on respective tear-drop and rhombic ferrite elements 90 and it) in the manner shown in FIG. 8. As in that arrangement, elements 90and 10d each lhave an axis Vof symmetry" and the windings crisscross such axis so that their axes formequal angles with it. In each, the windings are arranged for zero or minimum mutual inductance; and in each theorientation of the ferrite element .with its major axis parallel to the longitudinal centerline of the aircraft insures .that the windings have the same pickup characteristics.

Where Ythe ferrite element is located on the aircraft in a position where it is not centered ,with respect to the longitudinal centerline, the'angles between the axes of the respective windings and the longitudinal axis of the ferrite element diferrslightly in the position of the windings to eiect zero mutual inductance.

. is that the windings are disposedfto equalize or balance temperature Yand capacitanceelects between them. It will be noted that the open-circuit` magnetic pathsfor the two windings contain equal lengths of ferrite and equal air-gaps. With windings of -the'samedimensiong their stray capacitances arethe'same, in which case the capacitance effects between them are balanced. Also, since the temperature coeicients of 'equal lengths of the ferrite are equal, then with windings of equal dimensions dis' posed as in FIGS. 8-10, temperature effects in onepath are matched in the other, whereby. pickup characteristics for both windings remain equal.

What is claimed is:

g l. In combination'with an automatic direction nder receiver, a at oblong element of magnetic material, a pair ofl superimposed windings having equal inductancesV supported on said velement with their axes in a common plane and extending perpendicular to each other and parallel to edges of saidoblong element, said windings being positioned on said element so that there is no mutualV ber.

, 2. .In combination with an automatic direction finder having arturner to which input signals are to be applied, an antenna system comprising a thin solid magnetic ele# ment of uniform thickness between at surfacesV thereof, iirst and second antenna windings wound one over the other and about said element and on said hat surfaces, -V

said windings having equal inductances, portions of said windings being located on either side of a predetermined From the foregoing, it will be apparent thatthis inven- Noris this invention limited to any particular type of conducton`-v Instead of flat ribbon, the conductors could be conventional round wire, fiat braided wire, Litz wire,

Vprinted strips, or anyof numerous types.

The choice of wire and winding arrangement would be dictated by design factors, e.g. tivity.

windings having axes in the same plane, andpositioned so there is substantially no mutual inductance. In the case of antenna structures adapted for quadrantal error compensation, an additional requirement is that the ferrite element be elongated in one dimensionalong an axis of symmetry, and that the windings be disposed about such axis.

A further advantage to the arrangements of FIGS. 8-10 ,l shielding desired, and pickup sensi- What is essential is that the ferrite element be hat, and shaped to. permit turnsA to be wound thereon to form two' axis, said windings being positioned sothere is no mutual inductance when a magnetic field set up by a transmitter station threads said element', a goniometer device having iirst and second stator windings respectively' connected to said first and second antenna windings, said stator windings being displaced electrical degrees from each other, a rotor'for said goniometer device having a winding sup# ported thereon, said rotor winding being inductively coupled to the tuner, said rotor winding having induced a signal representing the vector addition of signals inwinding is reduced to zero, and indicating means operable in said position of said rotor to indicate the direction to the station.

3. A combination in accordance with claim 2, wherein equal portions of said windings are located on either side Y of an axis of symmetry parallel to said fiat surfaces.

4. 'A combination in accordance with claim 3, wherein f the axes of said antennaV windings form equal angles with said axis of symmetry.

5. An antenna structure comprising a flat magnetic element, said element having at least one axis of symmetry V.and being elongated in theV direction of said one axis, a

pair of windings supported one over the other on said element, said windings each having the same inductance,

said windings having their Vaxesin the same plane, said Velement being adapted to be positioned so that a magnetic held established by a transmitter station passes through said element in the direction of said plane, and said winding elongated in the directioniof flight of the aircraft, a pair of windings having equal inductances supported one over the other on said element with their axes in a common plane, a goniometer device having'rst and second stator windings disposed at right angles to each other, a rotor having a winding thereon coupled to the input of the receiver, a motor connected between the output of the receiver and said rotor, said element being positioned so that a magnetic field established by an automatic direction `finder transmitter station threads said element and induces signals in said windings, said stator windings causing a signal to be induced in said rotor winding which represents the position of said rotor relative to the station, and said receiver applying a signal to the motor to effect positioning of said rotor so that the signal in said rotor winding is reduced to zero, whereby the position of said rotor corresponds to the direction to the station.

7. The combination of claim 6 wherein said flat element of magnetic material is of oblong shape.

8. An antenna structure for use on a movable vehiclev including in combination, a thin magnetic element having ilat parallel surfaces and adapted to be mounted on the vehicle, said element being elongated in the direction of movement of the vehicle and being symmetrical about an axis extending in such direction, and a pair of windings having turns on said dat surfaces and having axes in the same piane, said windings being disposed with the axis thereof at an angle with respect to each other and with one winding being wound over the other, said windings having the same inductance and being disposed about said axis of symmetry so that the mutual inductance therebetween is substantially zero.

9. An antenna structure in accordance with claim 8 wherein said magnetic element is oblong, and one of said windings has turns extending parallel to the greater dimension of the element .and the other of said windings has turns extending perpendicular to the turns of said one winding and parallel to the shorter dimension of said element.

l0. An 4antenna structure in accordance with claim 8 wherein said magnetic element is pointed in the direction of movement of the vehicle and the axis of symmetry thereof bisects the angle between the axes of said windings.

ll. A directional antenna structure for use on a movable vehicle including in combination, a thin solid magnetic element adapted to be mounted in tixed'position on the vehicle, said element having ilat rectangular surfaces each having one pair of parallel sides which are parallel to the direction of movement of the vehicle, and a pair of windings about said element having turns extending across said fiat surfaces, said windings having axes iu the same plane and one winding being wound over the other, one of said windings having turns extending parallel to the direction of movement and the other of said windings having turns extending perpendicular to the direction of movement, said windings having the same inductance and being disposed so that the mutual inductance therebetween .is substantially zero.

References Cited in the file of this patent UNITED STATES PATENTS 2,297,466 Funke et al Sept. 29, 1942 FOREIGN PATENTS 751,138 Great Britain June 27, 1956 411,165 Italy July 17, 1945 "i" 'm f. 

